Thermally stable polyester fibers having improved dyeability

ABSTRACT

Thermally stable fiber-forming polyester having improved dyeability with disperse dyes are produced from dicarboxylic acids, or reactive derivatives thereof, glycols and small amounts of mixtures of compounds having a typical general formula: R-O(GO)x-H where R is an alkyl group containing an average of from about eight to 20 carbon atoms; G is a hydrocarbon radical selected from the group consisting of ethylene, propylene and isomers thereof, butylene and isomers thereof, and mixtures of the above; and x has an average value of from 8-20, and is about equal to or greater than R. Polyfunctional chain-branching agents in amounts up to about 0.73 mole percent, based on the weight of the dicarboxylic acid or ester-forming derivative thereof, may be added, whereby the polymer, with the chain terminators described above, can be polymerized to higher molecular weights by ordinary polymerization techniques.

United States Patent King et al. 51 June 6, 1972 s41 THERMALLY STABLE POLYESTER 3,033,824 5/1962 Huffman ..260/75 FIBERS HAVING IIVIPROVEI) 3,042,656 7/1962 Frey ..260/77 E I Y 3,223,752 12/1965 Tate et al ..260/873 3,461,468 8/1969 Morgan et a1. ..260/75 T [72] Inventors: Henry L. King; Eugene L. Ringwald, both of Cary, NC; James C. Randall, Bart- Primary Examiner-Melvin Goldstein lesville, Okla. Attorney-Thomas Y. Awalt, Jr. and Robert L. Broad, Jr. [73] Assignee: Monsanto Company, St; Louis, Mo. [57] ABSTRACT [22] Filed May 1969 Thermally stable fiber-forming polyester having improved [21] Appl. No.: 824,092 dyeability with disperse dyes are produced from dicarboxylic I acids, or reactive derivatives thereof, glycols and small Related pp Data amounts of mixtures of compounds having a typical general [63] Continuation-impart of Ser. No. 789,528, Jan. 7, FT RO[G O]I H where. R an alkyl gmup 1969 abandoned taming an average of from about eight to 20 carbon atoms; G is a hydrocarbon radical selected from the group consisting of 52 vs. C]. ..260/77 8/DIG. 4 ethylene Pmpylene and isomers butylene and [5]] lnhcl i ucasg 17/08 isomers thereof, and mixtures of the above; and x has an 58 Field ofSearch.... ..260/77 average value fmm 8-20 and is abut equal greater than R. Polyfunctional chain-branching agents in amounts up [56] References Cited to about 0.73 mole percent, based on the weight of the dicarboxylic acid or ester-forming derivative thereof, may be UNlTED STATES PATENTS added, whereby the polymer, with the chain terminators described above, can be polymerized to higher molecular 5,3; i Eat}: ..260/75 X weights by ordinary polymerization techniques a a U "13.11.. 2,905,657 9/1959 Huffman ..260/75 8 Claims, 11 Drawing Figures PATENTEDJUH 81972 3,668,187

SHEET 2 0F 4 O N 3 s L, 0 mm m k D 5 N 3 IW o w m .5 o w 5 2 .A n o OS O o 7 6 5 4 3 2 O 2 951225 232;; UMF WHP P 0 0 O I O 0 9 O N A 6S 0 O0 0000 O O U m 08 43 2 l 50 In H 25 52; 122E 4T 3 2 O O O O O O O O O 6 M 2 m 8 6 4 2 PPM PENTA FIG. 6.

INVENTORS HENRY L. KING EUGENE L. RINGWALD JAMES C. RANDALL BY w w.

ATTORNEY PPM TRIMESIC ACID FIG.5

SHEET 3 BF 4 PATENTEDJUH 6 I972 k 5 4 3 2 D l O 5 m 5 4 3 2 l O sw 7h mmzzwo \mz mw to zmk 40S ANHE m m 3 mm F 2TM w E P P .l 5 N 2 O 7 6 5 4 3 2 I O0 2 92 2210 232;; w w w THOUSANDS PPM TRIMESIC ACID FIG. 9.

INVENTORS HENRY L. KING EUGENE L. RINGWALC JAMES C. RANDALL BY z ,7 ATTORN Y HUNDREDS PPM PENTA FIG. 8.

500 PPM TRIMESIC 4 3 2 l mmzzmo $256 2325 SHEET 4 0F 4 250 PPM PENTA L250 PPM PENTA 2,500 PPM PENTA PATENTEDJUH 6 I972 IO l5 2O 25 ELONGATION /o FIG. ll.

INVENTO S HENRY L. KING EUGENE L. RINGWALD JAMES C. RANDALL BY %W W ATTORNEY THERMALLY STABLE POLYESTER FIBERS HAVING IMPROVED DYEABILITY This is a continuation-in-part application of our co-pending application, Ser. No. 789,528, filed Jan. 7, 1969 and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to polyesters produced by condensation reactions of polymethylene glycols and dicarboxylic acids or reactive derivatives thereof.

It is well known that the polymeric polyesters prepared by the condensation of a glycol or its functional derivatives and a dicarboxylic acid or a polyester-forming derivative thereof, such as an acid halide, a'salt, or a simple ester of a dibasic acid and volatile monohydric alcohol are excellent fiber-forming polymers. Commercially, highly polymeric polyesters are prepared, for example, by the condensation of terephthalic acid or dimethyl terephthalate and a polymethylene glycol containing from about two to carbons atoms, and particularly ethylene glycol. These polyesters are relatively insoluble, chemically inactive, hydrophobic materials capable of being formed into filaments which can be cold-drawn to produce textile fibers of superior strength and pliability. However, since these materials are not readily permeable to water, they cannot be satisfactorily dyed by ordinary dyeing procedures.

The compact structure of polyethylene terephthalate fibers, for example, the molecules of which are closely packed along the axis of the fibers, makes it quite difficult, except with a limited number or dyes, to obtain a high degree of dyebath exhaustion or to secure satisfactory deep shades. Absorption and penetration of the dye into the fiber core are limited by the inherent properties of the fiber.

A number of methods have been proposed to increase the dyeability of polyesters, and particularly polyethylene terephthalate; however, most have not proved to be entirely satisfactory. These methods have included the use of a number of additives to the polyester and various combinations of drawing and heat-treatment steps and procedures. Unfortunately, the use of most of these known procedures has resulted in thermally unstable polyesters, deterioration in fiber properties, nonuniformly 'dyed polymers, and the like. Finally, the art has desired some other means to produce thermally stable polyesters having improved dyeability. Thermally stable polyesters with improved dyeability would have significant commercial and practical value and utility.

SUMMARY OF THE INVENTION It is an object of this invention to provide a process for preparing synthetic linear condensation polyesters having improved dyeability with disperse dyes and thermal stability in the presence of oxygen.

It is another object of this invention to provide a new composition of matter comprising a synthetic linear condensation polyester which is easily dyeable with disperse dyes and is thermally stable in the presence of oxygen It is yet another object of this invention to provide a chainterminating agent suitable for the production of synthetic linear condensation polyesters with improved dyeability and with thermal stability in the presence of oxygen.

Briefly, the objects of this invention are accomplished by preparing a fiber-forming polyester from a dicarboxylic acid and a glycol and containing in the polymer molecule a small amount of compounds having a typical general formula: R- O[GO],,H where R is an alkyl group containing an average of from about eight to carbon atoms; G is a hydrocarbon radical selected from the group consisting of ethylene, propylene and isomers thereof, butylene and isomers thereof, and mixtures of the above; and x has an average value of from 8-20, and is about equal to or greater than R. Mixtures of these glycols may also be used. The monohydroxyl additive may be used at concentrations of between about 0.25 and 3 mole percent, based on the weight of the dicarboxylic acid or ester-forming derivative thereof or on each polyester repeating unit. Preferably, the additive is present in an amount of from about 0.75 to 2 mole percent, based on the weight of the dicarboxylic acid or ester-forming derivative thereof or on each polyester repeating unit. The use of less than 0.25 mole percent of the additive does not give any significant improvement in the dyeability in the final product, and when more than 3 mole percent of the additive is employed, undesirable quantities of chain-branching agents are necessary to counteract the tendency of the monohydroxyl additive to restrict the build-up of molecular weight in the final polymeric product.

The modified polyester compositions of this invention are prepared by reacting an aromatic dicarboxylic acid, the polymethylene glycol and a small amount of the glycol additive under polyesterification conditions until a fiber-forming polymeric polyester composition is obtained. Small amounts of a chain-branching agent may also be added to the reaction as desired.

The modified polyester compositions of the present invention are useful in the production of shaped articles by extrusion, molding, or casting in the nature of yarns, fabrics, films, pellicles, bearings, ornaments, or the like. They are particularly useful in the production of thermally stable textile fibers having improved dyeability, particularly with disperse dyes.

To further understand the invention, reference will be made to the attached drawing that forms a part of the present application.

FIG. 1 is a graph showing the amount of formaldehyde loss at 195 C. for 60 minutes of alkoxy polyethylene glycols varying in the number of ethylene oxide units present in the molecules;

FIG. 2 is a graph showing the relative disperse dyeability in terms of percentage of the dye based on the weight of the fiber, of polyester fibers modified with ethylene oxide polyethers in which carbon atoms in the alkoxy group represented by R in the general formula, was varied between four and 20, with the number of ethylene oxide units (x) constant at a value of 12-14;

FIG. 3 is a graph showing the relative disperse dyeability in terms of percentage of dye on the weight of the fiber, of polyester fibers modified with an ethylene oxide polyether in which the number of ethylene oxide units (x) was varied from between four and 30, with R constant at a value of from 12-14;

FIG. 4 is a graph showing the effect of a chain-branching agent, pentaerythritol, on processing time in the polymerization stage described below;

FIG. 5 is a graph showing the comparative effect of trimesic acid on the processing time in the polymerization stage;

FIGS. 6 and 7 show the effect on maximum draw ratios of the filament products, of various amounts of pentaerythritol and trimesic acid, respectively, as chain-branching agents;

FIGS. 8 and 9 show the effect of various amounts of pentaerythritol and trimesic acid, respectively, as chain-branching agents, on the tenacity of the filament products.

FIGS. 10 and 11 show stress-strain curves of various amounts of pentaerythritol and trimesic acid, respectively, as chain-branching agents.

Other objects and advantages of this invention will be apparent from the description which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The synthetic linear condensation polyesters contemplated in the practice of the invention are those formed from dicarboxylic acids and polymethylene glycols, and copolyesters or modifications of these polyesters and copolyesters. In a highly polymerized condition, these polyesters and copolyesters can be formed into filaments and the like and subsequently oriented permanently by drawing. Among the polyesters and copolyesters specifically useful in the instant invention are those resulting from heating one or more of the glycols of the series HO(CH,),,OI-l, in which n is an integer from 2 to 10,

with one or more dicarboxylic acids or ester-forming derivatives thereof. Among the dicarboxylic acids and ester-forming derivatives thereof useful in the present invention there may be named terephthalic acid, isophthalic acid, p,p-dicarboxybiphenyl, p,p-dicarboxydiphenylsulfone, p,p-dicarboxydiphenylmethane, and the aliphatic, cycloalphatic, and aryl esters and half-esters, ammonium and amine salts, and the acid halides of the above-named compounds, and the like. Examples of the polyhydric alcohols which may be employed in practicing the instant invention are ethylene glycol, trimethylene glycol, and tetramethylene glycol and the like. Polyethylene terephthalate, however, is the preferred polymer because of the ready availability of terephthalic acid or dimethyl terephthalate and ethylene glycol, from which it is made. It also has a relatively high melting point of about 250 C. through 265 C., and this property is particularly desirable in the manufacture of filaments in the textile industry.

The additives which are an essential part of this invention are compounds having a typical general formula: RO[G O],I-l where R is an alkyl group containing an average of from about eight to carbons atoms; G is a hydrocarbon radical selected from the group consisting of ethylene, propylene and isomers thereof, butylene and isomers thereof, and mixtures of the above; and x has an average value of from 8-20, and is about equal to or greater than R. By average is meant that the glycol additive may comprise mixtures of the glycol with some variances from the figures shown; but that the average of the integers in the mixture will be as indicated. Preferably, the R group contains l21 6 carbon atoms. The optimum degree of polymerization (x) is about 12-16. This additive may be used at concentrations of from about 0.25 to 3 mole percent, based on the weight of the dicarboxylic acid or ester-forming derivative thereof or on each polyester repeating unit. Preferably, the additive is present in amounts of from about 0.75 to 2 mole percent, based on the weight of the dicarboxylic acid or ester-fonning derivative thereof or on each polyester repeating unit.

The use of alkoxy polyethylene glycols as chain-terminators in the preparation of modified polyesters is not new (see, for example, US. Pat. No. 2,905,657). What is new and significant, with respect to the particular glycols described, is that within the described critical range of the alkyl group there is a suprisingly and substantially lower degree of autoxidation which takes place at elevated temperatures (as low as 150 C.). Moreover, there are new and distinguishable dyeability factors involved.

Autoxidation is the phenomenon which is responsible for much of our environmental chemistry. It is involved in the ageing of fats and oils, drying of paints, and degradation of natural and synthetic fibers. The processes involved may be catalyzed by heat or light and are free radical by nature. Generally speaking, autoxidation proceeds by free radical, chain mechanisms; peroxy radicals and hydroperoxide groups are formed which are precursors to other products. Typical products from autoxidation processes are alcohols and carbonyl-containing compounds. Chain-terminating reactions significantly affect the rates of autoxidation processes.

The products observed from the autoxidation of alkoxy polyethylene glycols are principally alcohol and formate ester chain terminal groups and formaldehyde, carbon dioxide, and water. Formaldehyde is a major volatile product. As above stated, significant and surprising differences in thermal stability in the presence of oxygen have been observed among the various alkoxy polyethylene glycols. The type of alkoxy unit and the degree of polymerization are apparently related to the susceptibility of autoxidation.

It has been found, for example, that as the number of carbon atoms in the alkoxy end group is increased beyond the methoxy (with degree of polymerization held constant) there is a surprising decrease in the amount of formaldehyde evolved when the glycol additive is heated in a sweep of air at 193 C., until the alkoxy group reaches eight carbon atoms, after which there is a leveling off. Further increase beyond eight to 14 carbon atoms in the alkoxy group causes no appreciable difference in the heat stability of the glycol. Exemplifying the above, hydrocarbon terminated polyethylene glycol polymers having the structural formula:

R(OCH,CH ),,OH

were subjected to the above-described conditions, and liberated formaldehyde in accordance with the following table.

"alkoxy polyether prepared from mixture of 14 and 15 carbon alcohols It was also discovered that when the same polyethylene glycols were used as chain terminators in the production of modified polyesters, the heat stability effect was carried over to the polyester fiber.

On the other hand, where the number of carbon atoms in the alkoxy end group was held constant at about 14 and the degree of polymerization of the polyether chain was increased, the compounds being heated in a sweep of air at C., for 60 minutes, there was a marked increase in the number of micromoles of formaldehyde released as the degree of polymerization (numer of ethylene oxide units) was increased from about 5 to 30, indicating a decrease in heat stability of the glycol as shown by FIG. 1. Therefore, so far as heat stability alone is concerned, and ignoring any possible effect of the relationship of the degree of polymerization to the length of the alkoxy end groups, it appears that an alkoxy po1y(oxyalkylene) glycol as described above where R is an alkyl group containing no less than eight nor more than about 20 carbon atoms, and with an extremely low degree of polymerization would be optimum.

As stated above, however, dyeability of the modified polymer is an extremely important factor so far as the use of these additives is concerned. In FIG. 2, the effect on fiber dyeability of changes in the number of carbon atoms in the alkoxy group (R) with the degree of polymerization (x) being held constant at 11-13 is shown; and in FIG. 3, the effect of changes in the degree of polymerization (x) with R being held constant at 14.5 is shown. FIGS. 2 and 3 show the disperse dyeability of these compounds in terms of percent dye on the weight of the fiber, dyeing being accomplished as explained in Example 1. It will be observed from FIG. 2 that there is a tendency toward decreased dyeability as the number of carbon atoms in the alkoxy end group of the additive increased. FIG. 3 shows a substantial increase in dyeability as the degree of polymerization (x) is increased from about 4 to about 12-14, and thereafter a decrease in dyeability.

A minimum optimum value of eight representing the number of carbon atoms in the alkoxy end groups has thus been established on the basis of heat stability, and a maximal optimum value of 20 has been established beyond which there is no increase in heat stability, but there is a corresponding decrease in disperse dyeability (FIG. 2).

The degree of polymerization has been established on the basis of dyeability with about 8 as a minimally marginal value and 20 as a marginally maximum value (FIG. 3), with decreasing heat stability across the range (FIG. 1). An additional limiting factor involving the relationship of R to x will be developed in the examples.

The precise structure of G is not considered critical in the instant invention except insofar as it must exclude the alkoxy(oxymethylene) glycols which depolymerize under polyester polymerization conditions. We have found that the alkoxy poly(oxyethylene), alkoxy poly(oxypropylene), and alkoxy poly(oxytetramethylene) glycols (including copolymers and block copolymers) and mixtures thereof produce good results in accordance with this invention.

The above can be partially explained in terms of inhibition of further autoxidation by products formed from the terminal alkoxy groups in the initial stage of oxidationfThose derived from short alkyl chains are volatile at the test temperature, and escape without acting as inhibitors.

Whenthe additive contains an alkoxy group which is an effective inhibitor of autoxidation, the number of alkyleneoxy units in the polyether additive becomes significant. It has been found that chains having more than about 25 units are not adequately stable. This is believed to result from the low concentration of the inhibiting terminal alkoxy group in such a chain. 0n the other hand, a low number of alkyleneoxy units per molecule results in an excessive number of chain terminations when an adequate weight of the modifier is added to achieve the desired dyeability. Poor processibility results from excessive chain termination.

Since the hydrophobic alkyl portion of the additive makes very little, if any, contribution to the enhanced dyeability, it is desirable that a major portion of the molecule be comprised of the hydrophilic polyether chain. Thus, alkoxy poly (oxyalkylene) glycols in which the number of oxyalkylene groups is about equal to or greater than the number of carbon atoms in the alkyl group, resulting in a polymer composed of more than 70 percent by weight of the hydrophilic polyether portion, as will be shown in the examples, are most effective (see Table III). Included within the meaning of about equal, as used herein, is:2.

If desired, the modified polyesters of this invention may contain chain-branching agents, which, as taught in U.S. Pat. No. 2,895,946, are employed to increase the viscosity or molecular weight of the polyesters, such as polyols which have a functionality greater than two, that is, they contain more than two functional groups, such as hydroxyl. Examples of suitable compounds are pentaerythritol; compounds having the formula: I

wherein R is an alkylene group containing from three to six carbon atoms and n is an integer from 3 to 6, for example, glycerols, sorbitol, l ,2,6-hexanetriol and the like; compounds having the formula:

R- (CH Ol-I) wherein R is an alkyl group containing from two to six carbon atoms, for example, trimethylol ethane, trimethylol propane, and the like compounds up to trimethylol hexane; and the compounds having the formula:

wherein n is an integer from 1 to 6. As examples of compounds having the above forrnula, there may be names 1,3,5- trimethylol benzene; l,3,5-triethylol benzene; 1,3,5- tripropylol benzene; 1,3,5-tributylol benzene; and the like.

Aromatic polyfunctional acids or their esters may also be employed in this invention as chain-branching agents, and particularly those having the formula:

and in which R. is H or an alkyl group containing one to three carbon atoms and x is an integer of 3 or 4. As examples of compounds having the above formula, there may be named trimesic acid, trimethyl trimesate, and tetramethyl pyromellitate, and the like. In addition, there may be employed mixtures of the above acids and esters which are obtained in practical synthesis. That is, in most instances, when preparing any of the compounds having the above formula, other related compounds having the same fonnula may be present in small amounts as impurities. This does not affect the compound as a chain-branching agent in the preparation of the modified polyesters and copolyesters described herein.

The chain-branching agents may be employed in the preparation of the polyesters and copolyesters in amounts ranging from 0 mole percent to 0.73 mole percent, based on the amount of dicarboxylic acid or ester-forming derivative thereof employed in the reaction mixture. If the chainbranching agent is tetra-functional, as for example, pentaerythritol, quantities not in excess of 0.45 mole percent should be used. The preferred concentration of a tetra-functional chain-branching agent is about 0.19 mole percent. If a trifunctional chain-branching agent, such as for example, trimesic acid, is used, somewhat more is required for results equivalent to that of the tetra-functional chain-branching agent, and amounts up to 0.73 mole percent may be used. The preferred concentration of a trifunctional chain-branching agent is 0.49 mole percent.

In the practice of the present invention, the dibasic acid or ester-forming derivative thereof, the glycol, and the alkoxy polyoxyalkylene glycol are charged to the reaction vessel at the beginning of the first stage of the esterification reaction, and the reaction proceeds as in any well known esterification polymerization. If desired, the chain-branching agent may also be charged to the reaction vessel at this time.

When preparing the polyester from an ester, such as dimethyl terephthalate, the first stage of reaction may be carried out at C. to C. and at a pressure ofO to 7 p. s. i. g. If the polyester is prepared from the acid, such as terephthalic acid, the first stage of reaction may be carried out at about 220 C. to 260 C. and at pressures of from atmospheric to about 60 p. s. i. g. The methanol or water evolved during the first stage of reaction is continuously removed by distillation. At the completion of the first stage, the excess glycol, if any, is distilled off prior to entering the second stage of the reaction.

In the second or polymerization stage, the reaction may be conducted at reduced pressures and preferably in the presence of an inert gas, such as nitrogen, in order to pervent oxidation. This can be accomplished by maintaining a nitrogen blanket over the reactants, the blanket containing less than 0.003 percent oxygen. For optimum results, a pressure within the range of less than 1 mm. up to 5 mm. of mercury is employed. This reduced pressure is necessary to remove the free ethylene glycol that is formed during this stage of the reaction, the ethylene glycol being volatilized under these conditions and removed from the system. The polymerization step is conducted at a temperature in the range of 220 C. to

300 C. This stage of the reaction may be effected either in the liquid melt or solid phase. In the liquid phase, particularly, reduced pressures must be employed in order to remove the free ethylene glycol which emerges from the polymer as a result of the condensation reaction.

Although the process of this invention may be conducted stepwise, it is particularly adaptable for use in the continuous production of polyesters. In the preparation of the described polyesters, the first stage of the reaction takes place in approximately three-fourths to 2 hours. The use of an ester-interchange catalyst is desirable when starting with dimethyl terephthalate. In the absence of a catalyst, times up to 6 hours may be necessary in order to complete this phase of the reaction. In the polymerization stage, a reaction time of approximately 1 to 4 hours may be employed with a time of l to 3 hours being the optimum, depending on catalyst concentration, temperature, viscosity desired, and the like.

The linear condensation polyesters, produced in accordance with the present invention, have specific viscosities in the order of about 0.25 to 0.6, which represent the fiberand filament-forming polymers. It is to be understood, of course, that nonfiber-forming polyesters may be produced by means of the present invention, which have a greater or less melt viscosity than that specified above.

Specific viscosity, as employed herein, is represented by the formula:

Time of flow of the polymer solution in seconds p7 TLawf 1 9 he o yen 11 5999 5 1 Viscosity determinations of the polymer solutions and solvent are made by allowing said solutions and solvent to flow by force of gravity at about 25 C. through a capillary viscosity tube. In all determinations of the polymer solution viscosities, a solution containing 0.5 percent by weight of the polymer dissolved in a solvent mixture containing 2 parts by weight of phenol and 1 part by weight of 2,4,6-trichlorophenol, based on the total weight of the mixture is employed.

The polyesters of this invention may be produced to form filaments and films by melt-spinning methods and can be extruded or drawn in the molten state to yield products that can be subsequently cold-drawn to the extent of several hundred percent of their original lengths, whereby molecularly oriented structures of high tenacity may be obtained. The condensation product can be cooled and comminuted followed by subsequent remelting and processing to form filaments, films, molded articles, and the like.

Alternatively, the polyesters of this invention may be processed to shaped objects by the wet-spinning method, wherein the polyesters are dissolved in a suitable solvent and the resulting solution is extruded through a spinnerette into a bath composed of a liquid that will extract the solvent from the solution. As a result of this extraction, the polyester is coagulated into filamentary material. The coagulated material is withdrawn from the bath and is then generally subjected to a stretching operation in order to increase the tenacity and to induce molecular orientation therein. Other treating and processing steps may be given the oriented filaments.

lf it is desired to produce shaped articles from the polyesters of the present invention which have a modified appearance or modified properties, various agent may be added to the polyester prior to the fabrication of the articles or those agents may be incorporated with the initial reactants. Such added agents might be plasticizers, antistatic agents, fire-retarding agents, stabilizers, and the like.

To further illustrate the present invention and the advantages thereof, the following specific examples are given, it being understood that these are merely intended to be illustrative and not limitative. Unless otherwise indicated, all parts and percents are by weight.

The following procedure was used to prepare the polymers in the examples. The charge was added directly to a standard polyester autoclave and the system was purged six times with nitrogen, allowing the pressure to rise to 150 p. s. i. g., and then releasing it slowly to atmospheric pressure each time. The maximum rate of heating was then applied to the closed system, and when the temperature inside the autoclave had reached 100 C. to 125 C., the stirrer was started. When the temperature of the outside wall of the autoclave had reached about 250 C. (the inside temperature being about 230 C. to 235 C. and the pressure being about 25 p. s. i. g.), the offvapor valve was adjusted to maintain these conditons of temperature and pressure. As the first distillate containing water and some ethylene glycol appeared, the esterification stage was considered to have started. The stirrer speed was set at 240 r. p. m. This esterification step usually took from about 40 to 60 minutes for completion, after which the pressure of the system was adjusted to atmospheric pressure. The heating rate was then increased until the temperature reached about 280 C. During this time, excess ethylene glycol was distilled off. An ethylene glycol slurry of titanium dioxide was introduced through an injection port when the inside temperature had reached about 260 C. to 265 C. Then the inside temperature was raised to about 280 C., the pressure was maintained at less than 2 mm. Hg and the polymerization continued until a polymer having a specific viscosity in the fiber-forming range between 0.30 to less than about 0.4 was formed. The polymer was extruded through a spinnerette, and the filaments obtained were drawn about 5 times their original length over a hot pin at about C.

The dyeing test used throughout the examples was as follow. Fiber was scoured and dried. One-half gram of fiber and 20 mls. of dye solution were placed in a small glass tube capable of withstanding internal pressure. The dye solution was prepared by mixing 250 mgs. of a disperse dye and 0.5 gram of a commercial dispersing agent in a 250 ml. volmetric flask together with an amount of deionized water sufficient to fill the flask to the mark. The dye tubes were placed in a rotating rack held within a steam bath, and rotated for two hours at a temperature of about 210 F. The tubes were then quickly quenched in ice, and 5 ml. aliquots were pipeted into 50 ml. volumetric flasks which were then filled with dimethylformamide. The optical density of each solution was measured in a 1 cm. cell at the dominant wavelength of the dye. A blank tube (dye only) was also prepared and its optical density measured in the same way. The percent dye uptake on weight of the fiber (o.w.f.) was calculated using the following equation:

concentration (percent)=percent dye uptake (o.w.f.)

X original dye During the processing of polyester filaments, staple, blends, fabric, and the like, heating at various temperatures for various periods of time is often necessary, e.g., polyester fabrics may be subjected to temperatures of 175 C. or higher for periods of up to 10 minutes or more. The following thermal stability tests were run where indicated. A 5-gram sample of the polyester was fluffed into a ball, placed in an aluminum cup into which about 10 half-inch holes had been punched, and the ball was heated for 10 minutes at 175 C. in a circulating-air oven, often with a thermocouple held at the center of the ball.

EXAMPLE 1 The autoclave was charged with 166 grams of terephthalic acid, 400 ml. of ethylene glycol, 0.078 gram of lithium sulfate, 0.967 gram of antimony trioxide, 0.20 gram of pentaerythritol, and 10 grams of methoxypolyethylene glycol having an average molecular weight of about 550. Polymer and fiber were prepared following the procedure described above.

The fiber took up 2.2 percent o.w.f. of Latyl Brilliant Blue 26 dye (C.I. Disperse Blue 61). Unmodified polyethylene terephthalate took up 0.6 percent o.w.f. of this dye.

The fiber fused severely when heated at 175 C. for 10 minutes, the thermocouple within the carded ball recording a temperature of 220 C.

EXAMPLES 2 8 Example 2 The autoclave was charged with grams terephthalic acid, 330 ml. ethylene glycol, 0.04 grams lithium acetate, 01 grams antimony glycoloxide, 0.3 gram pentaerythritol, and 8.0 grams of the reaction product of 4 molar equivalents of ethylene oxide with an approximately equimolar mixture of straight chain alcohols having 14 to 15 carbon atoms. Polymer and fiber were prepared following the procedure described in Example 1. Examples 3-8 were conducted in the same manner as Example 2 with the exception that the amounts of pentaerythritol used in each example were as follows: Example 3 0.15 grams; Example 4 0.2 grams; Example 5 0.25 grams; Example 6 0.25 grams; Example 7 0.25 grants; and Example 8 0.0 grams. The alkoxy poly(oxyalkylene) glycols used had the general fonnula:

for which the number of carbon atoms in the alkyl group R and the degree of polymerization of ethylene oxide (x) are shown in Tabl l": The resulting percent dye uptake is shown for each sample.

The aboveresults further substantiate the data shown in FIGS. 1-3, and establish the relationship between R and x which is theorized above. Example 4 was tested for heat stability and resisted fusion when heated at 175 C. for 10 minutes.

The following examples demonstrate in terms of polymer processability and fiber properties, the relationship between the concentration of typical chain-branching agents in the polymer described, using a chain-terminating agent in an amount of 1.2 mole percent, having a formula:

R-O(GO) ,I-I, where R is an alkyl group containing an average of 14-15 carbon atoms, G is an ethylene radical, and x is about 14.

The examples demonstrate the use of a typical tetra-functional alcohol, pentaerythritol, and trimesic acid, a typical trifunctional aromatic acid, as chain-branching agents. The polymer was prepared in a small batch autoclave using the procedures described above, spun through 10 hole spinnerettes, and drawn over a hot-pin at 70 C. The fiber was drawn at 90 percent of the maximum obtainable draw, and physical properties were determined on boiled-off fiber under standard conditions.

TABLE IV.-EXAMPLES CONTAINING PENTAE RYTH RITOL Mole P.p.m. percent Polymeri- PENTA ENTA zation DTA (based on (based on time m.p. Specific Example polymer) TA) (minutes) C.) viscosity This polymer, containing no chain-branching agent, could not be polymerized to a. higher molecular Weight so polymerization was discontinued alter 147 Initiates. QIZIIIIS polymer could not be successfully spun because of excessive cross- TABLE V.EXAMPLES CONTAINING TRIMESIC ACID 1 This polymer was difiicult to spin and could not be drawn because of 54 151144 19 e Fibers from these preparations were drawn at 90 percent of maximum attainable draw ratio and single filament Instron properties determined under standard conditions on the boiled-off fiber.

TABLE VI.PIIYSICAL PROPERTIES OF FIBER WITH PENTAE RYTIIRITOL BWS Tenacity, El0ng.. Mod- Max. percent I D PF gflL/dell. percent ulus draw 1 Boiling Water shrinkage. These fibers have not been previously heat set at temperatures above 100 0.

TABLE V1I.-PHYSICAL PROPERTIES OF FIBER WITH TRIMESIC ACID 1 3 o i 1i ng water shrinkage, fibers not previously heatset.

Although shrinkage data was not set forth on the above tables, it was found that those fibers having larger amounts of chain-branching agents have less shrinkage than those fibers having smaller amounts. at

The effects of the concentration of chain-branching agents in terms of processability in the polymerization stage, as reflected in Tables IV and V, is shown graphically in FIGS. 4 and 5, respectively. The times required to polymerize to a specific viscosity of approximately 0.30 is shown to decrease as the amount of chain-branching agent increases. With no chain-branching agent present, the maximum obtainable specific viscosity for the polymer was found to be about 0.286. With the pentaerythritol, as shown in FIG. 4, there is an exponential relationship between the rate of polymerization and the concentration of the chain-branching agent. With trimesic acid, however, there is a linear relationship as shown in FIG. 4.

The tetra functional chain-brancher, when completely reacted, can form two side-chains in contrast to the one formed with the trifunctional chain-brancher.

The effects of various concentrations of the tetra-functional chain brancher, shown at FIG. 6, and the trifunctional chainbrancher, shown at FIG. 7 on the maximum draw ratio, where the maximum obtainable draw ratio over a hot pin at 70 C. is plotted as a function of the concentration of the chainbrancher, reflects a decrease in both cases as the concentration of the chain-brancher is increased.

Fiber tenacity decreases as the concentration of the tetrafunctional chain-brancher increases (FIG. 8), and as the concentration of the trifunctional chain-brancher increases (FIG. 9). These linear relationships reflect that without a chainbrancher, a tenacity of about 5 grams/denier is possible at the drawing conditions employed. A good compromise (4 grams/denier in the case of the tetra-functional chainbrancher at a concentration of 1,250 ppm or 0.187 mole percent) is shown between processability and tenacity. As shown at FIG. 9, a tenacity of about 4 may be achieved using up to about 3,000 ppm of the trifunctional chain-brancher. The processability of the polymer in each case, as shown at FIGS. 4 and 5, at about 80 minutes and minutes, is considered relatively good.

Stress-strain curves of the fibers of some of these examples, as shown in FIGS. 10 and 11, reflect a decrease in breaking tenacity as the amount of the chain-brancher increases. It is noteworthy that at low elongation, 7-10 percent in the case of fibers containing the tetra-functional chain brancher, there is an increase in strength with an increase in the level of the chain-branching agent.

FIG. 4 shows that a level of between 2,000 and 2,500 ppm of the tetra-functional chain-brancher is required to induce a polymerization rate equivalent to that of an unmodified polyethylene terephthalate with a batch polymerization time of about 40-45 minutes for a 0.31 specific viscosity polyethylene terephthalate and between 5,000 and 7,500 ppm of the trifunctional chain-brancher. The strength of such fibers would be about 2 grams/denier less than the unmodified PET fibers.

Larger amounts of the trifunctional chain-branching agent are required in order to obtain the same level of processability. A polymer containing 1,500 ppm of the tetra-functional chain-brancher polymerized in 76 minutes (FIG. 4); and a polymer containing 5,000 ppm of the tri-functional chainbrancher polymerized in 77 minutes. The fiber containing the pentaerythritol had a tenacity of 4.05 grams/denier; and the fiber containing trimesic acid had a tenacity of 3.40 grams/demer.

As used herein the term filament" is generic, and not meant to exclude staple fiber.

wherein the synthetic linear condensation polyester has at least 85 percent by weight of an ester of terephthalic acid and ethylene glycol, and is further modified with up to about 0.45 mole percent, based on the amount of terephthalic acid, of a tetra-functional chain-branching agent selected from the group consisting of (a) compounds having the formula R- (OH). wherein R is alkylene group containing from three to six carbon atoms; and (b) aromatic tetra-functional acids or their esters.

3. The new composition of matter defined in claim 2 where the chain-branching agent is pentaerythritol.

4. A new composition of matter as defined in claim 1 wherein the synthetic linear condensation polyester is a polyester of terephthalic acid and ethylene glycol, and further modified with up to about 0.73 mole percent, based on the weight of the terephthalic acid, of a chain-branching agent selected from the group consisting of: (a) compounds having the fonnula R(OH) wherein R is an alkylene group conit is to be understood that changes and variations may be made in the present invention without departing from the sphere and scope thereof as defined in the appended claims.

We claim:

1. A fiber-forming disperse dyeable thermally stable linear condensation polyester consisting of at least 85 percent by weight of an ester of a glycol of the series HO(CH )n OH in which n is an integer from 2 to 10 and terephthalic acid, and modified with from 0.25 to 3 mole percent, based on each polyester repeating unit, of a chain terminating additive having a general formula R-O[GO],H, where R is an alkyl group containing about eight to 20 carbon atoms; G is a hydrocarbon radical selected from the group consisting of ethylene, propylene and isomers thereof, andbutylene and isomers thereof; and x is an integer having a value 8-20, and is about equal to or greater than the number of carbon atoms in R.

2. A new composition of matter as defined in claim 1 taining three to six carbon atoms; (b) compounds having the formula: R(CH OH) where R is an alkyl group containing from two to six carbon atoms (c) compounds having the formula:

wherein n is an integer from 1 to 6, and( d) aromatic trifunctional acids or their esters.

5. The new composition of matter defined in claim 4 wherein the chain-branching agent is trimesic acid.

The new composition of matter defined in claim 2 wherein the chain-branching agent is pentaerythritol, in an amount of about 0.19 mole percent, based on the weight of the terephthalic acid.

7. The new composition of matter defined in claim 4 wherein the chain-branching agent is trimesic acid in an amount of about 0.49 mole percent based on the weight of terephthalic acid.

8. A new composition of matter as defined in claim 1 wherein the additive is present in from about 0.75 to 2.0 mole percent, based on each polyester repeating unit, R is an alkyl group containing an average of 12-16 carbon atoms, G is an ethylene radical, and x is about 14. 

2. A new composition of matter as defined in claim 1 wherein the synthetic linear condensation polyester has at least 85 percent by weight of an ester of terephthalic acid and ethylene glycol, and is further modified with up to about 0.45 mole percent, based on the amount of terephthalic acid, of a tetra-functional chain-branching agent selected from the group consisting of (a) compounds having the formula R-(OH)4 wherein R is alkylene group containing from three to six carbon atoms; and (b) aromatic tetra-functional acids or their esters.
 3. The new composition of matter defined in claim 2 where the chain-branching agent is pentaerythritol.
 4. A new composition of matter as defined in claim 1 wherein the synthetic linear condensation polyester is a polyester of terephthalic acid and ethylene glycol, and further modified with up to about 0.73 mole percent, based on the weight of the terephthalic acid, of a chain-branching agent selected from the group consisting of: (a) compounds having the formula R-(OH)3 wherein R is an alkylene group containing three to six carbon atoms; (b) compounds having the formula: R-(CH2OH)3 where R is an alkyl group containing from two to six carbon atoms (c) compounds having the formula: wherein n is an integer from 1 to 6, and (d) aromatic trifunctional acids or their esters.
 5. The new composition of matter defined in claim 4 wherein the chain-branching agent is trimesic acid.
 6. The new composition of matter defined in claim 2 wherein the chain-branching agent is pentaerythriTol, in an amount of about 0.19 mole percent, based on the weight of the terephthalic acid.
 7. The new composition of matter defined in claim 4 wherein the chain-branching agent is trimesic acid in an amount of about 0.49 mole percent based on the weight of terephthalic acid.
 8. A new composition of matter as defined in claim 1 wherein the additive is present in from about 0.75 to 2.0 mole percent, based on each polyester repeating unit, R is an alkyl group containing an average of 12-16 carbon atoms, G is an ethylene radical, and x is about
 14. 